Evaporating apparatus



June 30, 1964 F. A. zENz EVAPORATING APPARATUS Filed Feb. 9, 1960 IN V EN TOR. Fnsvsmcn A. ZeNz B lll Il IIIIIIII.. VIIIIIJ ORNE Y United States Patent G 3,139,069 EVAPORATING APPARATUS Frederick A. Zenz, Bryant Ave., Roslyn Harbor, N.Y. Filed Feb. 9, 1960, Ser. No. 7,567 4 Claims. (Cl. 122-32) This invention relates to an improved vapor generating means and more particularly to a means for vaporizing a liquid at a higher capacity and with a greater efiiciency than is possible with conventional vaporizing apparatus.

If one considers the transfer of heat from a hot surface to a liquid as in a flame-fired heater or a steam coil immersed in the fluid, it is apparent that the hot surface is in contact with bulk liquid. The liquid is vaporized by the formation of bubbles on the hot surface which then tear loose and rise through the bulk liquid. When a bubble tears loose, liquid rushes into the space formerly occupied by the bubbles and hits the hot surface whereupon other bubbles are formed. Again, these bubbles tear loose and more liquid rushes in to contact the hot surface so that still more bubbles are formed. This process is repeated over and over again until all of the liquid is vaporized.

The transfer of heat from the hot surface to the fluid is usually interpreted in terms of a heat transfer coefficient expressed as B.t.u.s per hour per square foot per degree Fahrenheit of temperature difference between the hot surface and the iluid. Quite obviously, the hotter the surface, or more precisely the greater the temperature difference between surface and fluid, the faster the boiling or the greater the heat transfer coefiicient. However, there is a limit to the rate of heat transfer no matter how great the temperature differential. Measurements taken on the vaporization of a liquid by means of an immersed steam coil show that the heat transfer rate increases somewhat parabolically for increasing temperature differentials until a peak heat transfer rate is reached after which the rate starts to decline even though the temperature differential is increasing.

The decline after reaching a peak is the result of what could be called vapor binding. The heat transfer between a hot surface and a liquid is much greater than that between a hot surface and a gas or vapor. Under comparable conditions it is well known that the heat transfer coeicient for liquids range from several hundred to several thousand while those for gases range from ten to a hundred. At the peak heat transfer rate vapor bubbles are forming so rapidly that they cannot escape from the tube or hot surface fast enough to let more liquid take their place and as a result the hot surface becomes more and more in contact with gas or vapor rather than liquid. Since local heat transfer coefficients will therefore be dominated more and more by gas rather than liquid the overall effect is a continual decline with increasing surface temperature as noted above.

Contrasted to the foregoing a thin film of liquid will boil off at higher temperature differentials without the formation of bubbles and under such conditions the rate of vaporization approaches that expressed by the equation W: mspx/g 1) where Wis the rate of vaporization;

P is the vapor pressure of the liquid;

T is the liquid temperature; and

MW is the molecular weight of the liquid.

It is the object of this invention to provide an apparatus for vaporizing liquids according to the film boiling concept. In carrying out the invention a steam line or re tube 3,139,135!) Patented June 30, 1964 is immersed in the reservoir of liquid to be vaporized according to the principles of thin film boiling while liquid from the reservoir is vaporized in the conventional manner by contact with the outside of the steam line.

Features and advantages of this invention may be gained from the foregoing and the description of a preferred embodiment thereof which follows.

In the drawing:

FIGURE 1 is a schematic representation of a vaporizer embodying the principles of the invention;

vFIGURE 2 is a sectional view taken along Iline 2 2 of FIGURE l; and

FIGURE 3 is a fragmentary View showing another embodiment of the invention.

Referring to the drawing, `a pressure vessel 10 is shown holding a volume of liquid 11 that is to be vaporized. An inlet conduit 12 (schematically shown) is provided fot introducing liquid into pressure vessel 10. A tire tube 13 is shown through which steam or other heating fluid is brought into contact with the liquid to be vaporized.

The ire tube is shown entering the top of vessel 10, passing down through the liquid 11 and out the bottom of the vessel where it will generally lead to a condensate pump which removes any condensed heating fluid. A vapor pipe 14 is provided inside of and concentric with iire tube 13. This pipe is closed at its lower end and extends through the fire tube to the upper end of the pressure vessel above the surface of liquid 11.

A series of inlet ports 15 extend through tire tube 13 and vapor pipe 14 to carry liquid 11 from the reservoir to the inside of pipe 14. The ports are of such dimension that the liquid just seeps through and forms a high vaporization rate iilm on the inside of pipe 14. The computation of the aperture sizes for a lm formation on the inside of pipe 14 is well known to those skilled in the art and need not be reviewed here. Each of the inlet ports is surrounded by insulating material 16 so that the liquid enters pipe 14 and forms a film on the uninsulated portions thereof before it is vaporized. Otherwise a vapor lock may be formed to prevent the liquid from entering into pipe 14.

The liquid entering pipe 14 and forming a lm on the inner surface thereof will vaporize at a high rate as per Equation 1. The vapor will then rise in pipe 14 to the upper portion of vessel 10 whereupon it Will be delivered through the vapor outlet 17.

At the same time that lm boiling is taking place on the inside of vapor pipe 14, conventional boiling will be taking place on the outside of re tube 13. The vapor bubbles thus formed will rise through the liquid 11 in the reservoir to mix, in the upper portion of vessel 10, with the vapor rising through pipe 14. The baffles 20 shown on the outside of each of the seepage ports 15 prevent bubbles formed on the outer surface of tube 13 from interfering with the liquid flow into the ports. Since the vapor formed by conventional boiling is in the form of bubbles rising through the liquid in the vessel, there is considerable liquid droplet entrainment as the bubbles burst at the liquid surface. Consequently, if it is desired that the vapor be dry, the vapor emanating from pipe 14 can be kept separate from that produced by conventional boiling. See FIGURE 3, where vapor pipe 14 is shown directly connected to a second vapor outlet 21 which will then conduct vapor free of liquid droplet entrainment. Vapor produced by conventional boiling will, of course, be removed from vessel 10 through outlet 17. However, even if admixed the liquid droplet entrainment is much less than if the vapor is produced by conventional boiling alone. Thus less disengaging height of vessel 10 is required. Or there is less need for disengaging devices above the surface of liquid 11.

It is to be understood that the foregoing represents a plurality of steam coils or re tubes would be used rather than one as shown in the schematic drawing. Auxiliary equipment such as superheaters might also be used inY conjunction with the vapor generating apparatus, as well as condensers or turbine drives depending on the ultimate usefor which the vaporized fluid is intended.

Moreover the actual inlet ports might be slots rather than rounded apertures; the inner open ended vapor pipe might be movable to permit control of the port size; and the entire assembly might be tapered from bottom to top to accommodate greater vapor ow at the upper open end of the vapor pipe. Thus itis apparent that many changes could be. made in the apparatus described without departing from the spirit and scope of the invention and, therefore, it is intended that what is described in the specification and shown in the drawing be interpreted in an illustrative rather than a limiting sense.

' Moreover it is conceivable that the heat source might be self contained within the annulus between the lire tube 13 and the vapor pipe 14 as would be the case if it were filled with fissionable material such as uranium. A sutlicient array of such assemblies could thus constitute the core of a boiling-liquid-cooled nuclear reactor.

What is claimed is: f

1.7A Vapor generating apparatus comprising a vessel for containing a liquid to be vaporized, inlet means for introducing such liquid into said vessel, a vapor outlet located above the level to which the vessel is filled with a liquid to be vaporized, heat exchanger means disposed within said vessel so as to be surrounded by a liquid to be vaporized, said exchanger comprising a closed chamber, a vapor pipe disposed generally within said chamber and extending through one wall of said chamber to a i point above the level to which the vessel is filled with a liquid, the other end of said pipe being closed, a plurality of ports extending from the outside of said heat exchanger means to the interior of said Vapor pipe, said ports being of such dimension that the liquid passing therethrough forms a ilm on the interior of said pipe whereby the liquid is vaporized without the formation of bubbles, and

a re tube for carrying a heating fluid to said heat eX-V changer and the spent heating fluid away from said exchanger.

2. A vapor generating apparatus according toclam l including a second vapor outlet and wherein the vapor pipe extends directly to said second vapor outlet whereby the vapor produced in said vapor pipe is kept separate from that produced by conventional boiling and is essentially free of liquid entrainment.

3. A vapor generating apparatus according to claim l including insulating means surrounding each of said inlet ports whereby liquid will pass from the vessel and form a ilm on the interior of said pipe before being vaporized.

4. A vapor generating apparatus according to claim 1 including bale means disposed on the outer surface of said conduit below each of said inlet ports whereby vapor bubbles formed by conventional boiling of the liquid will be prevented from blocking seepage of the liquid through the inlet ports.

References Cited in the file of this patent UNITED STATES PATENTS 899,738 Kirkwood Sept. 29, 1908 1,886,135 Tannehill Nov. 1, 1932 1,993,674 Larsen Mar. 5, 1935 FOREIGN PATENTS 19,916 Australia Oct. 27, 1934 1,040,042 France May 20, 1953 

1. A VAPOR GENERATING APPARATUS COMPRISING A VESSEL FOR CONTAINING A LIQUID TO BE VAPORIZED, INLET MEANS FOR INTRODUCING SUCH LIQUID INTO SAID VESSEL, A VAPOR OUTLET LOCATED ABOVE THE LEVEL TO WHICH THE VESSEL IS FILLED WITH A LIQUID TO BE VAPORIZED, HEAT EXCHANGER MEANS DISPOSED WITHIN SAID VESSEL SO AS TO BE SURROUNDED BY A LIQUID TO BE VAPORIZED, SAID EXCHANGER COMPRISING A CLOSED CHAMBER, A VAPOR PIPE DISPOSED GENERALLY WITHIN SAID CHAMBER AND EXTENDING THROUGH ONE WALL OF SAID CHAMBER TO A POINT ABOVE THE LEVEL TO WHICH THE VESSEL IS FILLED WITH A LIQUID, THE OTHER END OF SAID PIPE BEING CLOSED, A PLURALITY OF PORTS EXTENDING FROM THE OUTSIDE OF SAID HEAT EXCHANGER MEANS TO THE INTERIOR OF SAID VAPOR PIPE, SAID PORTS BEING OF SUCH DIMENSION THAT THE LIQUID PASSING THERETHROUGH FORMS A FILM ON THE INTERIOR OF SAID PIPE WHEREBY THE LIQUID IS VAPORIZED WITHOUT THE FORMATION OF BUBBLES, AND A FIRE TUBE FOR CARRYING A HEATING FLUID TO SAID HEAT EXCHANGER AND THE SPENT HEATING FLUID AWAY FROM SAID EXCHANGER. 